The present invention relates generally to flow regulation apparatus, and more particularly, to a valve assembly adapted to permit substantially free flow through the valve in a first direction, while preventing flow through the valve in a second, opposite direction. Even more particularly, the present invention relates to valves commonly known as the "duckbill" type.
Duckbill valves have been known for some time and have been used in a variety of applications, several examples being shown in U.S. Pat. Nos. 3,822,720 and 3,901,272. Such a valve typically includes a housing into which is mounted a resilient flow regulator member having as its primary operative components a pair of lips arranged in a converging relationship from an open end at the base of the lips to a normally closed outer end. At the closed end of the regulator, the lips are located adjacent each other so as to define a normally closed slit therebetween. The regulator is mounted within the housing in a sealed relationship so that flow through the housing must pass through the regulator as well. In a first or forward direction, flow enters the housing and passes into the regulator through the open end, moving toward the normally closed end. The flow pressure against the resilient lips opens the slit, allowing the flow to pass out of the regulator and the housing. When flow enters the housing from a second or a reverse direction, however, flow contacts the regulator at its normally closed end, with the flow pressure against the resilient lips holding the slit in its closed position, thereby preventing flow through the valve assembly.
Frequently, valves of this type are used in medical environments, and one application for the valve is as part of a medical solution administration set. Such a set is used to deliver fluids such as plasma, medicines and the like from a fluid supply source, such as a bottle or bag, intravenously to a patient. The valve assembly is disposed within a fluid conduit to prevent flow in a backward direction toward the source, and is typically included in an administration set having a Y-site located downstream from the valve into which medicine or other fluids are injected at a pressure higher than the primary fluid flow.
One problem encountered with use of duckbill valves of conventional design in an administration set arises from the fact that whenever fluid flow is commenced through the valve, air bubbles typically collect around the valve assembly. Once fluid flow is established, these bubbles must be carried away with the fluid flow, so that they will not obstruct or interfere with the smooth and metered flow of fluid through the administration set.
A solution to this problem is described in commonly-assigned, U.S. Pat. No. 4,535,818 issued Aug. 20, 1985 in which a duckbill valve assembly similar to that shown in FIG. 1 is disclosed. Referring to this drawing, the assembly housing includes an outlet portion 10 and a cooperating inlet portion 12. Portions 10 and 12 are preferably molded from a transparent acrylic plastic material, although many other materials could be used, depending upon the particular application for the valve assembly.
A flow regulator member 14, molded as a single piece from a material such as rubber or resilient plastic, is formed in a roughly conical, hollow shape. A pair of lips 16 form a portion of regulator 14, each lip 16 having a base region 18 and an outer end 20. Lips 16 are disposed in a converging relationship so that lips 16 are adjacent each other at their outer ends 20. Lips 16 thus form a normally closed slit 22 to define a normally closed end for regulator 14.
Curved side walls 24 interconnect lips 16 and define an open end for regulator 14 opposite slit 22. An outwardly extending flange 26 is formed around the open end of regulator 16 adjacent the bases 18 of lips 16.
Outlet portion 10 of the housing defines a housing interior that approximates the shape of regulator 14. A pair of planar walls 28 forming part of outlet portion 10 define a pair of planar surfaces for the housing interior Planar walls 28 are arranged in a converging relationship toward an outlet end of portion 10, where an outlet port 30 communicates with the housing interior.
Planar walls 28 are interconnected by curved walls, and an annular collar 36 extends around the open end of outlet portion 10. As a result, an annular shelf is defined, so that regulator 14 may be positioned within the housing interior by placement of flange 26 against collar 36. When so placed, lips 16 are disposed substantially adjacent to, but not in contact with, planar walls 28 of outlet portion 10. Outer ends 20 of lips 16 are then located at the outlet end of portion 10, so that fluid flow passing through slit 22 is directed into outlet port 30.
The housing inlet portion 12 includes a circular cover plate 40 through which an inlet port 42 communicates. A sealing ring 46 extends perpendicularly around the periphery to cover plate 40. (It should be noted that, although the valve assembly is shown as substantially circular in cross-section, see e.g., cover plate 40, other configurations are also usable, such as oval, rectangular or square.)
After regulator 14 is placed within outlet portion 10, inlet portion 12 is positioned thereon so that sealing ring 46 surrounds annular collar 36. Inlet and outlet portions 10 and 12 are fastened together along the portions of sealing ring 46 and cover plate 40 that are in contact with annular collar 36, to provide a sealed housing for regulator 14.
Housing portions 10 and 12 may be fastened by a variety of methods. For example, a glue or adhesive may be applied along annular collar 36. However, since the valve assemblies are manufactured in large quantities, it has been found to be preferable to seal the housing portions 10 and 12 by ultrasonic welding, a process in which the parts to be joined are stimulated by ultrasonic vibrations to achieve sufficient atomic movement to cause coalescence.
As can be seen from FIG. 1, relatively little spacing is provided between lips 16 of regulator 14 and planar surfaces 28 of outlet portion 10 to discourage air bubble formation and to facilitate bubble clearance during fluid flow and initiation through the valve. This spacing between the housing interior and regulator may be as little as 0.001" (0.0025 cm). Consequently, it is necessary that the regulator be positioned within the housing with great accuracy, since only a relatively little misalignment of regulator 14 will cause the regulator to contact the interior surfaces of outlet portion 10. Due to the soft, resilient nature of regulator 14, any such contact will cause distortion of the regulator 14 with the result that slit 22 at the outer ends of lips 16 can be prevented from fully closing or being closed. This in turn prevents the valve assembly from completely preventing flow through the assembly in reverse direction.
As a practical matter, it is difficult to properly orient the regulator within the housing portion due to the close fit between regulator 14 and the housing interior. Misalignment that can bring the lips 16 of regulator 14 into contact with planar surfaces 28 of the housing interior, thereby causing slit 22 to be partially opened, can arise from a number of causes. For example, such misalignment of the regulator can be rotational. However, misalignment can also be caused by regulator 14 being placed into housing portion 10 at a slightly off-center position, or at a slight angle with respect to the horizontal (with respect to FIG. 1).
Moreover, it has been found that the misalignment need not even be so severe as to bring the lips of the regulator into contact with the housing interior. Slight misalginments will cause distortions in the flange of the regulator when it is secured into place between the housing portions. Due to the very soft material from which the regulator is constructed, these distortions can be transmitted from the flange to the lips, where the distortions can prevent the lips from fully closing.
In any of the cases above, even though all the parts used in the valve assembly are fault free, the valve assembly as manufactured may fail to prevent flow in a reverse direction, thereby exhibiting leakage.
What is needed, therefore, is a modification to the assembly structure of a duckbill valve that will prevent unwanted misalignment of the regulator within the valve housing during assembling of the housing. Specifically, modifications are needed that will prevent misalignment caused by the valve regulator being positioned within the housing off-center or at an angle with respect to horizontal. Such modifications should not affect the ability of the valve assembly to prevent air bubble formation and facilitate bubble removal during flow initiation, nor should they interefere with valve assembly manufacturing procedures so as to complicate or make more expensive production of such assemblies.